1. Industrial Field of the Invention
The present invention relates to a rotary head type magnetic recording/playback apparatus (hereinafter referred to simply as a VTR) (VTR: Video Tape Recorder) in which a magnetic tape is wound around a cylindrical rotary head cylinder, having a rotary head built therein, over a predetermined angle to record/playback a signal by the rotary head, and more particularly, to a VTR in which a magnetic tape is automatically withdrawn out of a tape cassette having a supply reel and a take-up reel provided therein, and wound around the rotary head cylinder over a predetermined angle.
2. Description of the Prior Art
Recently, various kinds of trials have been made for reducing the size, weight and height of VTR. In particular, because a mechanism of loading a magnetic tape in VTR has a very complicated arrangement, needs a large number of parts, and affects the size of the entire VTR to a considerable degree, development of the loading mechanism is quite important.
A conventional arrangement of VTR, particularly, an arrangement for positioning a pair of magnetic tape withdrawer units during completing a tape loading operation, will be described below with reference to drawings (see JP-B-57-23334).
FIG. 19 is a top plan view showing an arrangement of VTR after completion of a tape loading operation. In FIG. 19, 101 denotes a cassette having a supply reel and a take-up reel provided therein. A magnetic tape is wound around the both reels and extends, via guide posts 105a, 105b and 106, between the both reels.
The cassette 101 is rested on a base plate 110 at a predetermined position, the supply reel in the cassette 101 is fitted over a supply reel stand 111, and further the take-up reel is fitted over a take-up reel stand 112. 162 denotes an eraser head, 163 a control head, 164 a motor for a capstan and so forth, 165 a capstan and 166 an idler. I and II are a pair of magnetic tape withdrawer units for withdrawing the magnetic tape out of the cassette 101 and winding the same along the circumference of a rotary head cylinder 113 provided in an inclined position.
Denoted by 136 and 137 are loading rings turnably disposed on the underside of the base plate 110 one above the other in a concentric relationship.
In the magnetic tape withdrawer unit I, 114 denotes a withdrawer unit base arranged to be slidable in and along a guide slot 119 formed in the base plate 110. 120 denotes a vertical withdrawer pin provided on the withdrawer unit base 114 to withdraw the magnetic tape out of the cassette 101 and, after completion of a tape withdrawing operation, to serve as one guide pin for defining a running path of the magnetic tape.
The withdrawer unit II is constituted symmetrically to the withdrawer unit I and thus will not be described herein.
125 and 125' denote stoppers for limiting respective positions where an operation of the withdrawer units I and II for withdrawing the tape is completed. As shown in FIGS. 20 and 21, the stopper 125 comprises an upper projection 127 having a V-shape recess 126 which serves as a first stopper means, and a lower projection 161 having a U-shape recess 128 which serves as a second stopper means, the both projections being provided to oppose to each other. A flat plane c-c' passing through the center line a-a' of the V-shape recess 126 and the center line b-b' of the U-shape recess 128 is normal to the upper surface of the base plate 110. The U-shape recess 128 has a width s almost equal to the diameter of the vertical withdrawer pin 120 so that the pin 120 may fit into the recess 128 as indicated by phantom lines. An inclined cam surface 132 of the stopper 125 guides a projection piece 118 provided on the withdrawer unit base 114 so as to easily enter a recess 133 which serves as a third stopper means of the stopper 125, when the withdrawer unit I is slid toward the stopper 125 in a direction of an arrow X as shown in FIG. 22, while withdrawing a magnetic tape 104. The stopper 125' is exactly symmetrical to the stopper 125 and thus will not be described herein.
The manner of the magnetic tape withdrawer unit I precisely abutting against the stopper 125 will be next explained with reference to FIGS. 23A-23C. FIGS. 23A and 23C are a top and a bottom plan views of the stopper 125. The withdrawer unit I is moved with rotation of the loading ring 136 to approach the stopper 125 along the sliding guide slot 119 because a boss 116 is snugly fitted into the sliding guide slot 119. Then, the vertical withdrawer pin 120 first abuts against the V-shape recess 126 of the projection 127 serving as the first stopper means. At this time, with the boss 116 snugly fitted into the sliding guide slot 119, the vertical withdrawer pin 120 precisely abuts against the center of the V-shape recess 126 for proper positioning without laterally swinging to the left and right. Next, although force tending to continuously push the vertical withdrawer pin 120 still exists, the upper portion of the vertical withdrawer pin 120 is restricted in its further movement by the V-shape recess 126 and, therefore, only the lower portion of the vertical withdrawer pin 120 is pushed to raise the projection 118 of the distal end of the withdrawer unit I upwards. Thus, the projection piece 118 is brought into abutment against the upper inner surface of the recess 133, serving as the third stopper means of the stopper 125, to be held in a horizontal condition. The lower portion of the vertical withdrawer pin 120 snugly fits into the U-shape recess 128 of the projection 161 serving as the second stopper means, thereby restricting a lateral swing of the lower portion of the vertical withdrawer pin 120 to the left and right.
As explained above, the vertical withdrawer pin 120 is restricted in its position by the V-shape recess 126, the U-shape recess 128 and the upper inner surface of the recess 133, respectively serving as the first, second and third stopper means, in all the directions, i.e., laterally, to and fro, and vertically, so that the vertical withdrawer pin 120 may be held correctly normal to the base plate 110. Under a playback or recording condition, accordingly, the magnetic tape 104 can be brought into proper contact with the rotary head cylinder 113 while engaging with the vertical withdrawer pin 120. Note that operation of the vertical withdrawer pin 120' takes place in the same manner as the vertical withdrawer pin 120 and thus will not be explained herein.
However, the above conventional arrangement has suffered from such a first problem that the structure for positioning of the withdrawer units I and II is quite complicated, the number of parts used is very large, and the extremely high machining precision of respective components is needed to ensure a stable tape running system at all times, thus inviting limitations in reduction of the size, weight, height and manufacturing cost of the loading mechanism.
Stated otherwise, to restrict the positions of the withdrawer units I and II in all the directions, i.e., laterally, to and fro, and vertically, there are necessary the V-shape recess 126, the U-shape recess 128 and the upper inner surface of the recess 133, respectively serving as the first, second and third stopper means, which require a considerable degree of machining precision.
Next, in a conventional VTR, a gear for driving a loading gear comprises a two-stages gear. Two gears making up the two-staged gear are interconnected by a coil spring disposed around the axis such that one gear serves to drive the two-stages gear and the other gear serves to transmit driving force of torque to the loading gear. With this arrangement, when a loading post driven by the loading gear is stopped by a stopper, the one gear is rotated to a larger extent than the other gear against the coil spring to thereby produce force of pressing the loading post against the stopper.
By way of example, in Japanese Patent Application No. 1-267329 (corresponding to JP-A-3-127373 (published on May 30, 1991)) previously proposed by the inventors, as shown in FIG. 24 attached here, a torque of a cam gear 201 is transmitted to a loading main gear 204 through a gear 202 and a gear 203. The torque is further transmitted to a first loading gear 206 through a gear 205 fixed to the same shaft as the loading main gear 204 and, simultaneously, to a second loading gear 209 through a gear 207 and a gear 208 fixed to the same shaft as the gear 207. The loading gears 206 and 209 respectively drive ring gears 210 and 211 on which loading posts (not shown) are provided. In that mechanism, the pair of gears 204 and 205, and gears 207 and 208 each comprise a two-stages gear and are interconnected by respective coil springs 212 and 213 disposed around their axes. The coil spring 212 between the gears 204 and 205 and the coil spring 213 between the gears 207 and 208 take no part in driving the first loading gear 206 and the second loading gear 209, but after the loading posts moving together with the ring gears 210 and 211 are stopped by respective stoppers (not shown) at positions where an operation of loading a magnetic tape is completed, those springs are extended as the gears 204 and 207 further rotate to some extent, whereby the loading posts are resiliently pushed against the stoppers under action of respective spring forces for positive holding of the loading posts.
However, the above conventional VTR has suffered from such a second problem that resiliently pushing the loading posts needs one bias means for each of the loading post at the side of supplying the magnetic tape to the rotary head cylinder and the loading post at the side of taking the magnetic tape out of the rotary head cylinder and, therefore, requires a larger number of gears, which results in enlargement of the height and the area occupied by components. Especially in the case of using a pair of two-stages gears fitted with springs, that problem becomes severer and more disadvantageous in achieving reduction of the size, weight and height.
Moreover, in a conventional VTR, after finishing a loading operation to wind a tape around a cylinder drum having a rotary, a mode shift operation to effect a state of playback, stop, fast forward drive, etc. is effected. Then, the so-called driving force switching mechanism or intermittent motion mechanism is required to effect such a mode shift operation by using the same motor as that for the loading operation. As that type intermittent motion mechanism, use is made of the so-called geneva mechanism.
According to JP-A-63-61442, for instance, a cam gear 224 has a three-stages structure comprising a cam surface portion 224b, an intermittent gear portion 224c and a full-toothed gear portion 224d as shown in FIG. 25 attached here. Also as shown, a geneva gear 225 which is held in mesh with the cam gear 224 and makes an intermittent rotative motion for each turn of the cam gear 224, has a two-stages structure comprising a cam surface portion 225b and a full-toothed gear portion 225c. Torque is transmitted from a motor (not shown) to the cam gear 225 through the full-toothed gear portion 224d and the geneva gear is driven to operate following rotation of the cam gear.
A process of the intermittent motion in the above mechanism will now be explained in detail with reference to FIGS. 26A to 26F which are bottom plan views with relation to FIG. 25.
In a state of FIG. 26A, since the cam surface 225b of the geneva gear 225 is locked by the cam surface 224b of the cam gear 224, and the full-toothed gear portion 225c of the geneva gear 225 is not engaged with the intermittent gear portion 224c of the cam gear 224, the geneva gear 225 will not rotate and remains still. When the cam gear 224 is rotated in an anti-clockwise direction from the state of FIG. 26A to shift into a state of FIG. 26B, a tooth 225c of the geneva gear 225 starts engaging with one tooth 224e of the cam gear 224. When the cam gear 224 is further rotated in the anti-clockwise direction, the geneva gear 225 starts rotating in a clockwise direction as shown in FIG. 26C. After clockwise rotation of the geneva gear over an angle somewhat smaller than 360.degree. both the gears shift into a state of FIG. 26D. When the cam gear 224 is further rotated in the anti-clockwise direction, a tooth 225e of the geneva gear is disengaged from one tooth 224e of the cam gear, while a part 224f of the cam surface portion 224b of the cam gear raises up the cam surface portion 225b of the geneva gear as shown in FIG. 26E, followed by shifting to a state of FIG. 26F. When the cam gear 224 is rotated in the anti-clockwise direction from the state of FIG. 26F, the geneva gear 225 will not rotate and remains still because the cam surface portion 225b of the geneva gear 225 is held in engagement with the cam surface portion 224b of the cam gear 224.
By utilizing the above intermittent motion mechanism such that the cam gear is driven by the motor and a loading gear adapted to directly drive the loading post is held in mesh with the geneva gear, the mode shift motion can be performed using the same motor after finishing and before starting the loading operation of the magnetic tape.
However, the above driving device for the loading posts has suffered from such a third problem to be solved by the present invention that since the so-called geneva mechanism is used as the intermittent motion mechanism, the cam gear has the three-stages structure comprising a cam surface portion, an intermittent gear portion and a full-toothed gear portion, which is extremely disadvantageous in reducing the size, weight and thickness of the entire device. Further, use of the geneva gear is disadvantageous in not only that it has an increased thickness because of the two-stages structure comprising a cam surface portion and a full-toothed gear portion, but also that the geneva gear itself is too small to drive the loading post by itself and, eventually, the loading gear for driving the loading post must be meshed with the geneva gear (not shown). Accordingly, force or displacement must be transmitted from the cam gear, as a prime mover part, to the loading gear through one member in the form of a geneva gear, which is additionally disadvantageous in reducing the size, weight and number of parts used.